1. Field of the Invention
The present invention generally relates to semiconductor and micro fabrication equipment and, more particularly, to the integration of sensor technology within existing semiconductor and micro fabrication equipment for process control.
2. Background of the Invention
Semiconductor and micro fabrication equipment is designed to accept one or more cassettes of wafers. These wafers are the basic material which the majority of process equipment operate upon.
Wafers are automatically and individually loaded by a handling robot into the process tools from the storage cassette. The wafers are then processed. Following processing, the wafers are removed from the process tool by the handling robot and individually returned to the storage cassettes for removal and transport to the next phase of processing. Examples of next phase processing include photolithography tools, plating tools, chemical vapor deposition (CVD) tools, plasma etch tools including reactive ion etch (RIE) tools and chemical mechanical polish (CMP) tools. The processes listed above are typically controlled by a variety of measurement tools designed to accurately measure one or more of the process parameters and feed such parameters back to the process as a control input.
In the case of an oxide CMF process, silicon dioxide coated wafers are polished to a target thickness. To assure that the process is running under control, a wafer is periodically removed and its oxide thickness is measured externally with an optical thickness probe. The wafer is then returned to the process flow for further processing. Polish time is adjusted, if errors are found, to compensate and bring the process under control. This Send Ahead Measurement (SAHD) typically requires about five (5) minutes to perform, and is performed on a frequent basis.
A similar situation exists when using blanket copper plating for back end semiconductor wiring levels. In this process, a wafer is coated with a blanket layer of copper to a desired or xe2x80x9ctargetxe2x80x9d thickness. Again, the wafers are periodically removed to an external tool where the copper thickness is determined by performing an electrical sheet resistance measurement using a four point resistance probe. This SAHD process also takes significant time to perform.
The need to remove the product from the manufacturing process tool and perform ex-situ measurements occurs frequently and at a significant cost in terms of process time, handling and capital equipment. However, as metrology equipment decreases in size, it is increasingly desirable to integrate the equipment into the process tools to save process cycle time and redundant wafer positioning systems. This integration, while desirable, is often not possible due to the nature of the process tool, itself. This is because wafer access may be difficult to impossible within the process tool.
It is therefore an object of the present invention to provide an apparatus which integrates a variety of compact measurement equipment into semiconductor and micro fabrication process tools.
According to the present invention, there is provided an apparatus with one or more dimensions conforming to those of a standard wafer storage cassette containing all or part of a measurement sensor designed to measure a parameter of a wafer placed into the cassette. The intended use of the apparatus is in a process tool location normally occupied by a standard wafer cassette. By integrating all or part of the sensor into a standard wafer storage cassette a solution is provided whereby the same cassette and metrology system can be mechanically integrated into many process tools. This integration eliminates the need to modify the process tool to accommodate new sensor technology and allows the benefit of in process measurement of a parameter (such as film thickness) without removal mid-handling of the wafer to separate equipment.